Cluster formation of alpha7-containing nicotinic receptors at interneuronal interfaces in cell culture

Nicotinic receptors containing the alpha7 gene product are among the most abundant in the nervous system. Because of their widespread distribution and high relative permeability to calcium, the receptors regulate a diverse array of cellular events. On chick ciliary neurons the receptors are concentrated on somatic spines folded into discrete mats on the cell body and are overlaid by a large presynaptic calyx. The receptors co-localize with filamentous actin and the actin-associated protein drebrin which are concentrated in the spines. We show here that embryonic ciliary ganglion neurons grown in dissociated cell culture express and concentrate the receptors in large clusters or plaques that form at interneuronal interfaces between small clumps of neurons. The receptors resist detergent extraction even after disruption of the actin cytoskeleton, suggesting the importance of additional molecular mechanisms determining receptor location. The cell adhesion molecules N-CAM and N-cadherin are concentrated at the receptor plaques and may influence plaque stability. Although ciliary neurons do not normally contact each other in vivo, they do so in culture and may mimic interactions normally occurring between calyx and soma in vivo. As a result the cultures may prove useful for identifying components shaping development of postsynaptic specializations on neurons.